1. Field of the Invention
This invention pertains generally to apparatus and method for recording angle of inclination of a radiographic cassette, and more particularly to recording angle of inclination of a radiographic cassette with a digital inclinometer.
2. Description of Related Art
Knowledge of the angle of inclination of an imaged object can be extremely important for interpretation of object states. Accurate interpretation of imaging studies by a diagnostic radiologist, particularly x-ray studies of the chest and abdomen, requires knowledge of the patient state at the time of image exposure. For example, the thorax, abdomen, or other body part of a patient is typically oriented from 0° to 90° relative to the ground at the time of an imaging study, often a conventional x-ray. The vector force of gravity exerted upon imaged structures that are mobile (for example soft tissue structures, gaseous particles, and liquids) will vary according to the angle of inclination of these structures with respect to the gravitational force.
Conventional x-ray studies are currently presented for interpretation in a 2-dimensional format, either on film or a computer monitor, effectively flattening the anterior-posterior diameter of the imaged object. A device that accurately reports the angle of the photoreceptor at the time of imaging (in the case of diagnostic radiology, the film or imaging cassette 10 as shown in FIG. 1) enables more informed analysis of a 2-dimensional image, because the relative effect of the gravitational force can be integrated into its interpretation. Without knowledge of patient positioning, interpretation of diagnostic imaging studies is limited and can in fact be misleading. Clinical management often relies heavily on radiographic interpretations in patients ranging from the critically ill hospitalized patient to the ambulatory outpatient.
Portable x-rays are taken on the wards by radiology technologists with a portable x-ray device 12, shown in FIG. 2. A storage tray within this device contains multiple digital or film-based cassettes 10 which are transported back to a centralized digitizer 14 (FIG. 3) once exposed. Imaging cassettes typically range from approximately 10.5×10.5 inches to 13×15 inches or larger. Most cassettes are constructed from thick plastic-like material.
Standard digital imaging cassettes contain either a photostimulable phosphor plate or scintillator that ultimately converts x-ray photons into light. In the processing of digital imaging cassettes, the amount of light (proportional to incident x-ray exposure) is recorded and a digital file containing the two dimensional image matrix is generated. Film-based cassettes may be digitized subsequent to standard film processing.
The digitizer typically houses a computer terminal for entry of patient information (name, medical record number, ward, study indication, etc.) and image information (x-ray type, exposure energy, etc.). This can be done either manually by keyboard entry, or frequently automatically by barcode-type scanning of the imaging study requisition printout. Digitizers are designed to be “drop-and-go” devices that allow the technologist to insert the cassette, wait a moment for the imaging plate to be processed and erased, then either insert the next cassette or move on to the next task.
Digital files are created by the digitizer and transferred via network communications to the hospital PACS (Picture Archiving and Communication System) for viewing on a monitor by the radiologist. Standards for information exchange related to an imaging study have been established by the National Electrical Manufacturers Association (NEMA) in collaboration with radiologists, termed Digital Imaging and Communications in Medicine (DICOM). These DICOM standards allow the PACS system to recognize the various components of the imaging file (name, medical record number, study accession number, exposure parameters, etc.) in order to display these data for initial interpretation, subsequent archival, and later retrieval (of utmost importance for transferring studies to other institutions and for comparison with prior studies at a later date).
Referring to FIG. 4, some brands of digital cassettes 10 contain a built-in chip 16 that stores a unique identification number for each cassette. The cassette identifier number is typically uploaded to the digitizer by radiofrequency or other mode of wired or wireless data transmission for cassettes when inserted into the digitizer.
Currently, imaging cassette angle is measured, but only crudely and inconsistently. A commonly available imaging angle detector consists of a small plastic reservoir (shallow cup) containing three small metallic balls. Many radiology technicians performing x-ray examinations, film-based or digital, carry such a marker. If the balls are grouped together in the middle of the circle, it is presumed that the patient is flat (supine). If layered at the bottom of the reservoir, then it is assumed that the imaging cassette (and thus the patient) is in an elevated position with a wide range between 1° and 90°. Patient position may also be crudely indicated by the radiology technologist obtaining the x-ray. Radioopaque markers may be placed over the imaging cassette crudely indicating patient position using an arrow or labels, such as “supine,” “upright,” or “semi-erect.” For the diagnostic radiologist, these inconsistent and non-standardized techniques render the current method of cassette angle reporting relatively ineffectual.
Accordingly, an object of the present invention is to provide imaging angle detection and reporting to complement current radiographic imaging, and thus improve imaging technique and interpretative/diagnostic accuracy.
A further object is an imaging cassette with an indicator that signals prior exposure of the cassette array to x-rays.
At least some of these objectives will be met in the invention described hereafter.